The coating of substrates, e.g., glass, by cathode sputtering in plasma processes is well known. The sputtering can be done conventionally or using a reactive gas, which is called reactive sputtering. In the sputtering, a power supply produces a plasma, which removes material from a target, and the removed target material is then coated on a substrate, e.g., a glass substrate. If a reactive process is used, the target atoms can combine with gas atoms or molecules, depending on the desired coating.
In particular, if reactive processes are being used, arcs can occur in the plasma process. Such arcs can be detrimental to the plasma process and can even destroy the coating. Therefore, it is necessary to detect arcs quickly and reliably. Often, arcs are detected by monitoring an output voltage of the power supply. If there is a rapid fall in the output voltage, an arc is detected. Alternatively, the current can be monitored. If there is an instant rise in the output current, this is also indicative of an arc. In particular, each of the output current and the output voltage of the power supply can be monitored and compared with a respective threshold value.
Often, when an arc is detected, the power supply is turned off, so the arc is quenched. Turning off the power supply results in lower deposition rates. Therefore, the turn-off of the power should be as short as possible but as long as needed to avoid generation of another arc. In the following, the turn-off time before the power is switched on again is called a break time. For different processes and cathodes being used, different break times after arc detection are needed. It is known, to set break times by a user. However, it is difficult to set a proper break time. As mentioned before, the break time should be long enough for hot spots to cool down, so as to avoid new arc generation. On the other hand, the break time should be as short as possible to avoid unnecessary power losses during the plasma process.